sort_characters.py

# Given an arbitrary string:
#  1. count the occurrence of the characters `abcdefghijklmnopqrstuvwxyz_` in the string
#  2. sort the set of characters in the original string by their count of occurrences 
#  3. return the substring prior to the `_` character in the sorted string 

def problem(string):
    #valid characters 
    chars_to_count = 'abcdefghijklmnopqrstuvwxyz_'
    # dictionary to keep track of character counts
    # looks like {'a': 100, 'b': 300, ...}
    count = {}
    #loop over each character
    for char in list(string):
        if char in chars_to_count:
            #if already been counted, increment
            if char in count:
                count[char] += 1
            #if not, set value to one
            else:
                count[char] = 1

    #create a list of tuples 
    #looks like [(100,'a'), (300, 'b'), ...]
    tups = [(count[x], x) for x in count.keys()]

    #sort in decending order based on counts
    #looks like [(300, 'b'), (100,'a'), ...]
    sorted_tups = sorted(tups, reverse=True)

    #create answer from the sorted tuples by stopping concatenation before `_` character
    answer = ''
    #loop over each tuple
    for tup in sorted_tups:
        #if at the terminating character return
        if tup[1] == '_':
            return answer 
        #if not at end, add character to answer
        else: 
            answer += tup[1]
    
    # if down here, no '_' in input string 
    return 'Error: no \'_\' in input string'

#string to count
string = """ 
epqiiqwdiwgyka_vsqtsujeqqicnhyivo_sigwasmkwgsih_akl_gtnkhgikgveidpmt
qybpxpnnpbxkwpisgjmdzgh_ojysbtsnsvxvuhguocp_qc_vouxqmg_cetlpmounxnvg
ldcpem_jodnmklgonocekdkjwkdoilajk_nxujykigsolengqmnqofpseqaamvpsooga
spyhoojennefwvljpvsqtgnceg_hsowqvycjkuxdtfbxfloewkphmvkftjlsasvwid_u
qcsgn_ypiqjytygiwyziqdjpxgpuunymadnclpdlmmulitsnqlwciotbmyfuummjynne
slnit_lpykdafkpydzkntbud_gigjgmu_uqjjmdzpwteodjpuzndxaqmsjdjjamnwoes
ajcffkaaoilpyydlkyxauagfcjbabapax_ndlgtpwnud_jpnkiokviqjhyopmjtgtbyo
iyfbjdhknimlah_cxfzwspqoscffiyvabtjjuc_liaqbcuomuytdqfy_xaixiiqqdpds
uuimzh_ywwcmodxhfxjplyixotjkeawauxltekptuieekpbokbanumffatbtiacnywhw
iqxebnosninpzfjmatvnyuspyeu_ziapvogconld_cxfcytkcp_bvsppz_dw_ndlpkhf
zdlxbo_vaflmailjvccgsuclyhojganjqxzmqflpze_hqhlul_ybaagtiuokbzaxhmec
olsptiexvvmhbdoelgmcffulcebhlyzd_m_qxkbfvnxykdudpxefsm_aqpqtnhxvswht
owqnbm_mgejjpyumm_mqbkiuulanbmzllmuqlfftmcxtybmijfuwaknefhekwgujpjqg
leu_sjtbszotcygiclkwcbmnvgsoqaqqkkgeaslhvfbtlgpnxgpzxp_vyjinlwwfbvtn
twogmnpxghabpxxgzlyirrrrrbbcrrrnbjpcrrrqykhrrrscarrrdnlxrrrrtudrrrr_
ntrbyrqlddbycypcccqongpgexhnabavrmebeofrxsnrilprveetxaranjyfmrisrewp
r_y_lgsrsedbn_rfrieusemhpfa_plkifjipvwaqvnenrrrzybsrbeurbhfrvrrzghr_
zpgiyrrrqsnnrrrbhvdrrrqkpdrraqvkeueszfpkj_fm_claw_oetbgurbdocb_rsnzr
cyvrvnrvaurbscimurtbriikrfdjlizribdjwkror_gnlzmshwccqcx_huaafbvituxo
ru_hohxwrrrhnbttrrriyyirrrnibricrxftrrrrvqvrrrrhjorehroldibsmquelwvy
jebkolbbnauompgqdhlbnsfbbdiudoeibwstdg_acsazhtgfufidogmyvtya_dfwihto
elucbtlcbaijlcuhfvhesgluiwttsdnqqshnoqumccyqtko_zh_fii_wlsspysdqdpad
fvfewlsojavmuaixyxpw_xcwxuatceosdqgmsbbagjmmblouvnywmqqakmmtuasfovol
_ogksdukwp_fkxuh_vfhuhfyfvvfqhqxecxsoctcqgpianhtnkbqlltwyhxotfksoewm
elxobjgwlyfaeoxsfohhguidoftbsainwovvglynsgjixon_nvuwflsfbca_xnnesvco
mceh_gigjxpllckcooagidcpbqxtnejlnlsccocuvcvge_fvjjbyqdkjceia_mkcvbzl
zwlxbdjihvpmdcvmssuvktwiqbeivtieol_bu_huumzmlxx_kd_vksmohgzl_fxwfdue
lqgfkgzxciwmuduozfbaxstxkwegescggkpxfpeenhb_whqhethcateqdvnxhpt__bja
_uiyxchmfkblmdwtyp_ktontmufw_isdflelsbgjizxvqbciuadfxxjaqbluofkgkkkh
jbvohisfla_cspbmuezqohnyijyimwgdeszutgnaoagbhku_wwdtylbbiyvbpoumgyid
w_xwg_fkogabccip_wouclnjcgdpwwxxvvvwkmmbgfeactbcksxqovqthtjfjghijwwh
ydfieyssbjtfqgqyjnmwfpesljmwapvbptucadontbobnspch_i_dxheklulncdsdnic
bnjjjedkaokw_ahcolvbcnmqtoakonpgzjufqlnn_uve_uumaufjasfvfcv_cbcuk_hd
zigkahchzfqjphjwcbjwmozyodhu_tsqtafwidgmc_snhhkleyvmzdtawdodzfmekuee
mnshz_xz
"""
#run function with string
word = problem(string)

#output result
print 'The answer is: ' + word